Originally Posted by Lepomis
Vinegar (acetic acid) is not used to test a rocks "acidity". Vinegar is typically used to test for calcium carbonate containing rocks.
Alright let me correct myself here,
Rocks such as limestone can contain CaCO3 which can cause the Ph in the water to rise, CaCO3 is an alkali compound which acts as a neutralizer to the acid (vinegar), when an acid is poured on the rock the calcium carbonate neutralizes the acid therefore making it bubble.
Sorry its been forever and a day since science class